1. Field of the Invention
This invention relates to an improved pneumatic or hydraulic gripper assembly of the type generally employed in conjunction with a jack mechanism and arranged to surround a column, caisson or the like for raising and lowering a base or platform such as an oil drilling rig to be supported by the caissons above a body of water.
2. Prior Art
A substantial number of prior art devices of the type to which the present invention relates, are available. These prior art mechanisms can be broken down into two basic types, the first of which is constructed almost entirely of metallic parts which are linked together by hydraulic cylinders to provide the desired jacking action. Such a device is disclosed in the Lucus U.S. Pat. No. 2,841,961.
The second type of device is one which uses inflatable annular ring members which, when inflated, urge either metallic or rubber like grippers into gripping relationship with the caisson. A device of this type utilizing the rubber like gripper members is disclosed in Slemmons U.S. Pat. No. 3,844,002.
The present invention relates more to the second of these two basic types in that it is concerned with the use of inflatable members used to urge the gripper pads into engagement with the caisson.
Although jacking mechanism of this second type have been and still are used advantageously in supporting and jacking platforms such as those used for establishing off shore oil drilling platforms and the like, there are certain disadvantages associated with these devices which are overcome by the present invention.
One such disadvantage is that the inflatable member which urges the gripper assemblies into contact with the caisson, are annular in shape much the same as an inner tube for a tire. Because these jacking mechanisms are placed over the caissons and surround them entirely it becomes a difficult procedure to replace one of the inflatable annular members on the gripper assemblies without removing the entire jacking mechanism from the caisson. This requires a substantial amount of labor in that normally the jacking mechanisms are welded or otherwise securely anchored to the platforms. In order to remove one of the jacking mechanisms a temporary holding device must be secured between the platform and the caisson and then the jacking mechanism unfastened and lifted up off of the caisson and lowered onto the platform where it may be disassembled and a new inflatable member or gripper pad inserted. The jacking mechanism is then reassembled and placed back on the caisson and welded or otherwise secured to the platform and the temporary securing device removed, before the jacking mechanism can again be used to operate the platform again. This has proven to be substantially troublesome and time consuming in the erection of a platform.